1. Technical Field
The present invention relates to an electronically controlled mechanical timepiece and an overcharge-prevention method therefor. More particularly, the invention relates to an electronically controlled mechanical timepiece having a mechanical energy source, a generator for outputting electrical energy and being driven by this mechanical energy source and by generating induction power, a storage device for storing the electrical energy output from the generator, and a rotation control device for controlling the rotation period of the generator and being driven by the electrical energy supplied from the storage device. The invention also pertains to an overcharge-prevention method for the electronically controlled mechanical timepiece.
2. Background Art
In general, regular replacement of batteries is required for timepieces. These days, however, easy-to-handle and environmentally friendly timepieces are known in which the replacement of batteries is eliminated by charging power generated by a generator, such as an oscillating weight, a mainspring, a solar cell, etc., in a storage device, such as a capacitor or a secondary cell, and by using the charged power as a driving source.
Among such generators for use in timepieces, unlike a solar cell, a generator for generating power by rotating a rotor by a mainspring is not subject to constraints, such as environment, place, time, and so on, and can stably and reliably generate power by a user winding the mainspring. Accordingly, the above type of generator is widely used.
Electronic apparatuses using a mainspring generator include, for example, an electronically controlled mechanical timepiece. In the electronically controlled mechanical timepiece, mechanical energy generated when a mainspring is unwound is converted into electrical energy by a generator. A rotation control device is operated by this electrical energy so as to control the current value flowing in a coil of the generator, thereby correctly driving the hands fixed to a wheel train. As a result, the time can be correctly displayed. According to this type of timepiece, by detecting the generated waveform of the generator, the rotational speed of the rotor is determined, and braking control is performed so that the rotational speed (phase) of the rotor is matched to the speed (phase) of a reference signal from a time standard source, which is formed of a quartz oscillator, thereby implementing the indication of the correct time, which is the basic function of the timepieces.
The storage device for charging the generated power has a withstand voltage, and exceeding the withstand voltage of the storage device causes a deterioration in the characteristics, such as a decreased capacitance, or destruction and leakage due to expansion, which may lead to a fault in the timepiece having a built-in generator.
Thus, in order to prevent an unusual surge of the charging voltage of a storage device, a circuit, such as the one disclosed in Japanese Unexamined Patent Application Publication No. 21-236332, is used for a generator which generates power by the oscillation of an oscillating weight or a generator using a solar cell. According to this circuit, the voltage of the storage device is detected by a comparator, and when the voltage reaches a predetermined value, both ends of the generator are short-circuited so as to prevent any further current from flowing into the storage device. By the provision of this type of circuit, with an increase of the voltage of the storage device, the generator is short-circuited so as to interrupt the supply of power to the storage device, thereby preventing overcharging.
In the circuit disclosed in Japanese Unexamined Patent Application Publication No. 21-236332, however, since both ends of the generator are short-circuited, the waveform generated at both ends of the generator is deformed or the voltage level is reduced. Accordingly, by integrating the circuit disclosed in Japanese Unexamined Patent Application Publication No. 21-236332 in the above described electronically controlled mechanical timepiece, the rotational speed of the rotor cannot be correctly determined from the generated waveform, thereby failing to perform control of matching the rotational speed of the rotor to the reference signal of the time standard source. As a result, the time cannot be indicated correctly.
Accordingly, it is an object of the present invention to provide an electronically controlled mechanical timepiece in which overcharging of a storage device can be prevented and in which the time can be correctly indicated, and also to provide an overcharge-prevention method for the electronically controlled mechanical timepiece.
The present invention provides an electronically controlled mechanical timepiece including a mechanical energy source, a generator for outputting electrical energy and being driven by this mechanical energy source and by generating induction power, a storage device for storing the electrical energy output from the generator, and a rotation control device for controlling a rotation period of the generator and being driven by the electrical energy supplied from the storage device, the electronically controlled mechanical timepiece being characterized by comprising: a bypass circuit connected in parallel with the storage device with respect to the generator; a bypass circuit switch provided for the bypass circuit; and a voltage detection circuit for controlling this bypass circuit switch on and off according to a voltage of the storage device.
The electrical energy output from the generator is input into the storage device and is stored therein. In the present invention, the bypass circuit is provided in parallel with the storage device. Thus, when the voltage detection circuit turns on the bypass circuit switch of the bypass circuit according to the voltage of the storage device, the bypass circuit conducts so as to allow the electrical energy from the generator to flow into the bypass circuit. Accordingly, the current input into the storage device can be decreased so as to reduce the voltage of the storage device, thereby preventing the overcharging of the storage device.
Moreover, the input current into the storage device can be decreased without short-circuiting the generator so as to eliminate a deformation of the generated waveform and a reduction in the voltage level, thereby obtaining a generated waveform corresponding to the rotation period of the generator. Accordingly, since the rotation period of the generator can be correctly obtained from the generated waveform, the rotation period of the generator can be controlled highly precisely and reliably based on this generated waveform, thereby implementing the indication of the correct time.
An increase in the voltage of the storage device decreases the charging current into the storage device, and the braking effect is weakened, making it difficult to reserve the total required braking amount. In the present invention, however, when the voltage of the storage device exceeds the set voltage, the charging current flows into the bypass circuit, thereby interrupting the voltage surge of the storage device. A decrease of the braking effect, which would be caused by the charging current flowing into the storage device, can thus be prevented from being weakened, thereby reserving the overall required braking amount.
Additionally, when the timepiece is set in a test mode in which braking is not applied, the rotor may rotated at a high speed (for example, from two to ten times higher than the normal rotational speed). In this case, a generated current greater than a normal current is supplied from the generator to the storage device so as to increase the voltage. According to the present invention, however, an increase in the voltage can be prevented by allowing the charging current to flow in the bypass circuit, which serves as a limiter.
Further, since the voltage increase of the storage device can be prevented, the lifetime of the electronically controlled mechanical timepiece is prolonged. More specifically, in the electronically controlled mechanical timepiece, by reducing the wear of the mechanical energy source, such as a mainspring or the like, to a smallest possible level, the lifetime of the electronically controlled mechanical timepiece can be prolonged. In order to achieve this, the driving speed of the generator is desirably decreased to a minimal level. In this case, since the induction power is also reduced according to the decreased driving speed of the generator, it is also necessary to decrease the consumption power of the IC forming the circuit portion of the rotation control device, the voltage detection circuit, or the like which is driven by this induction power. In order to reduce the consumption power of the IC, it is necessary to reduce the thickness of the gate oxide film of the IC, which reduces the withstand voltage of the IC. This also requires that the voltage applied to the IC from the storage device should be suppressed to a lower level. In the present invention, therefore, since the voltage increase of the storage device can be prevented by the bypass circuit, an IC having a low withstand voltage, i.e., low power consumption, can be used as the IC forming the rotation control device or the like which is operated by the voltage from the storage device. Thus, in the electronically controlled mechanical timepiece, the provision of the bypass circuit in parallel with the storage device is very significant and meaningful because the driving speed of the generator can be decreased and the lifetime of the electronically controlled mechanical timepiece can be prolonged.
In this case, the rotation control device may preferably be provided with a circuit opening/closing device for disconnecting both terminals of the generator or for connecting the terminals in a closed loop state. As the rotation control device, a variable resistor or the like may be connected to the generator so as to change the current flowing in the coil of the generator, thereby adjusting the rotational speed. However, the circuit opening/closing device for switching between the closed loop state and the open loop state by connecting and disconnecting both terminals of the generator may be used. In this case, a closed loop may be formed across the terminals of the generator so as to apply braking by short-circuiting, thereby making it possible to perform brake control. It is thus possible to simplify the configuration of the rotation control device and to easily perform rotation control.
The rotation control device may preferably comprise control means for performing chopping control so that an opening/closing period in which the circuit opening/closing device is repeatedly connected and disconnected is shorter than a period of a rotation reference signal, which is a reference for the rotational speed of the generator. In this case, the voltage can be increased by chopping, thereby enhancing the induction power and also performing efficient brake control.
Moreover, the bypass circuit may preferably be disposed closer to the storage device than the circuit opening/closing device with respect to the generator. If the bypass circuit is disposed between the generator and the circuit opening/closing device, the circuit opening/closing device cannot perform rotation control while the bypass circuit switch is connected. If, however, the bypass circuit is disposed closer to the storage device than the circuit opening/closing device, i.e., at the side opposite to the generator with respect to the circuit opening/closing device, rotation control of the generator can be performed regardless of whether the bypass circuit switch is connected or disconnected. Additionally, the overcharging of the storage device can be reliably prevented.
The electronically controlled mechanical timepiece may preferably comprise a rectifier circuit for rectifying a current output from the generator, and the bypass circuit may be disposed closer to the storage device than the rectifier circuit with respect to the generator.
In this case, too, the bypass circuit does not interrupt the rectifying operation performed on the current output from the generator, and also, the overcharging of the storage device can be reliably prevented.
Further, a first end of the storage device may preferably be connected to a first end of the rectifier circuit connected to the generator, and a second end of the storage device may preferably be connected to a second end of the rectifier circuit, and the bypass circuit may preferably be disposed closer to the storage device than the circuit opening/closing device and the rectifier circuit with respect to the generator.
In this case, the bypass circuit does not interrupt the rotation control operation performed by the circuit opening/closing device and the rectifying operation performed by the rectifier circuit, and the overcharging of the storage device can be reliably prevented.
Still further, the first end of the rectifier circuit may preferably be formed of a first rectifier switch disposed between a first alternating current input terminal of the generator and the first end of the storage device, and a second rectifier switch disposed between a second alternating current input terminal of the generator and the first end of the storage device, and the circuit opening/closing device may preferably be formed of a first circuit opening/closing switch connected in parallel with the first rectifier switch, and a second circuit opening/closing switch connected in parallel with the second rectifier switch.
By separately providing a rectifier switch for the generator and a circuit opening/closing switch for switching both terminals of the generator between a disconnecting state and a closed loop state, rectify control and rotation control by the circuit opening/closing switch can be independently performed, thereby making it possible to easily perform both controls.
Additionally, the voltage detection circuit may desirably be driven by an output of the storage device. This obviates the need to provide a driving source specifically used for the voltage detection circuit, thereby enhancing the simplicity of the structure.
The voltage detection circuit may desirably be driven at regular intervals. By driving the voltage detection circuit intermittently in this manner, the consumption current of the voltage detection circuit can be reduced compared to when the voltage detection circuit is constantly driven, thereby enabling the efficient charging of the storage device.
Moreover, the voltage detection circuit may preferably be constantly driven when a detected voltage of the storage device exceeds a set value and the voltage detection circuit may preferably be driven at regular intervals when the detected voltage is not greater than the set value.
If the voltage detection circuit is driven at regular intervals, it is necessary that the resistance of the bypass circuit be increased to a certain degree in the case where the bypass circuit is turned on, so that the voltage does not considerably drop before the voltage is subsequently detected. This impairs the capacity of the bypass circuit for allowing the current to flow therein, and when the bypass circuit is connected because the voltage of the storage device exceeds a set value, it takes time to reduce the voltage to the set value.
On the other hand, as in the present invention, by constantly driving the voltage detection circuit when the voltage of the storage device exceeds a set value, the bypass circuit switch can be immediately turned off so as to interrupt the current from flowing into the bypass circuit when the voltage is reduced to the set value. It is thus possible to prevent the voltage of the storage device from being excessively reduced and to enhance the capacity of the bypass circuit for allowing the current to flow therein by reducing the resistance of the bypass circuit. The voltage detection circuit is driven at regular intervals when the voltage of the storage device is not greater than the set value. Accordingly, the consumption current when the voltage is low can be reduced, thereby making it possible to efficiently charge the storage device.
In this case, the voltage detection circuit may preferably comprise a comparator for turning on the bypass circuit switch when the detected voltage of the storage device exceeds the set value and for turning off the bypass circuit switch when the detected voltage is not greater than the set value, and a latch circuit disposed between this comparator and the bypass circuit switch so as to retain an output of the comparator.
The latch circuit is constantly operated so as to retain an output of the comparator. Consequently, the output of the comparator is retained by the latch circuit regardless of whether the comparator is on or off, i.e., even in the state in which the comparator is off, and the output from the latch circuit to the bypass circuit switch is continuously obtained.
More specifically, in the state in which the voltage detection circuit is off while it is driven at regular intervals, the output of the comparator to the bypass circuit switch is also discontinued. In this case, it is considered that the bypass circuit switch may be changed to a state different from the one instructed by the comparator. For example, when the bypass circuit switch is changed from the on state to the off state in the case where the voltage detection circuit is off, the bypass circuit is disconnected from the generator, which may make it difficult to sufficiently reduce the voltage of the storage device. On the other hand, when the bypass circuit switch is changed from the off state to the on state in the case where the voltage detection circuit is off, the bypass circuit is connected to the generator, which may reduce the charging efficiency of the storage device.
In contrast, in the present invention, the output of the comparator can be retained in the constantly driven latch circuit. Thus, the control state of the bypass circuit switch instructed by the comparator can be maintained even while the voltage detection circuit is turned off, thereby enabling highly precise and efficient on/off control of the bypass circuit switch.
In this case, the latch circuit may be operated according to a latch signal, and this latch signal may preferably be output at a first time interval (for example, every two seconds) when the voltage of the storage device is not greater than the set value, and the latch signal may preferably be output at a second time interval (for example, every one millisecond), which is shorter than the first time interval, when the voltage of the storage device exceeds the set value.
In this case, when the voltage of the storage device exceeds the set value, the output change of the comparator can be immediately reflected on the output from the latch circuit, thus making the circuit exhibit good response characteristics.
Also, the voltage detection circuit may preferably comprise voltage-dividing resistors for dividing the voltage of the storage device and for inputting the divided voltage into the comparator, a resistor switch for interrupting the supply of electrical energy from the storage device to the voltage-dividing resistors, a comparator switch for interrupting the supply of the electrical energy from the storage device to the comparator, and a drive unit for turning on the resistor switch and the comparator switch at regular intervals, and the comparator may preferably detect the voltage divided by the voltage-dividing resistors and compares it with the set value.
By providing the voltage-dividing resistors as described above, the voltage of the storage device is divided and is detected by the comparator. Then, the voltage input into the comparator can be adjusted according to the type of comparator. For example, when the set value (reference voltage) of the comparator is defined, the resistances of the voltage-dividing resistors are changed according to the magnitude of the set value so that the input voltage can correspond to the comparator. This enables the use of various known comparators.
As described above, the bypass circuit may desirably be provided with a resistor having a predetermined resistance. By providing this resistor, the charging current from the generator flows into the bypass circuit so as to decrease the current input into the storage device, and also, the charge stored in the storage device is discharged via the resistor so as to reduce the voltage of the storage device, thereby preventing the overcharging of the storage device more effectively.
The resistance may preferably range from about 100 kxcexa9 to 10 Mxcexa9 when, for example, a 10 xcexcF capacitor is used as the storage device, though it may vary by the capacitance of the storage device. If this resistance is an excessively small value, the charge stored in the storage device immediately after the bypass circuit switch is connected excessively flows into the bypass circuit, thereby causing a sharp voltage drop of the storage device. This sharp voltage drop may cause the occurrence of abnormalities and the stoppage of the electronically controlled mechanical timepiece. If the resistance is an excessively large value, the charging current flowing in the bypass circuit is decreased, and thus, the charging current flowing into the storage device cannot be significantly decreased, thereby hampering the degree of voltage reduction in the storage device. Thus, the resistance of the resistor is set so that the current flowing into the resistor is greater than the current flowing in the storage device so as to decrease the charging current flowing in the storage device, and that the voltage of the storage device does not sharply drop. With this arrangement, the current input into the storage device can be considerably reduced, and the charge of the storage device can be discharged, thereby efficiently reducing the voltage of the storage device in a short time.
Moreover, the bypass circuit may be provided with a diode. By providing a diode, the charging current from the generator is allowed to flow into the bypass circuit so as to prevent the overcharging of the storage device. It is also possible to prevent the current from flowing into the bypass circuit from the storage device immediately after the bypass circuit switch is connected, thereby preventing a sharp voltage drop of the storage device.
The bypass circuit may be part of the voltage detection circuit. The voltage detection circuit may preferably be provided with voltage-dividing resistors for dividing the voltage of the storage device, and the bypass circuit may preferably be formed by these voltage-dividing resistors.
By forming the bypass circuit as part of the voltage detection circuit, such as voltage-dividing resistors for dividing the voltage of the storage device, it is not necessary to specifically provide a resistor for the bypass circuit. This makes it possible to reduce the number of devices forming the circuit so as to make the circuit scale smaller, thereby achieving the miniaturization of the circuit and a reduction in the consumption power and the cost.
An overcharge-prevention method of the present invention is a method for an electronically controlled mechanical timepiece which includes a mechanical energy source, a generator for outputting electrical energy and being driven by this mechanical energy source and by generating induction power, a storage device for storing the electrical energy output from the generator, and a rotation control device for controlling a rotation period of the generator and being driven by the electrical energy supplied from the storage device. The overcharge-prevention method is characterized in that a bypass circuit is connected in parallel with the storage device with respect to the generator; and that the bypass circuit is electrically connected only when a detected voltage of the storage device exceeds a set value so as to decrease an input current into the storage device.
In this invention, the bypass circuit is electrically connected only when the detected voltage of the storage device exceeds the set value so as to input the electrical energy from the generator into both the storage device and the bypass circuit, thereby decreasing the input current into the storage device. With this arrangement, the voltage of the storage device can be restricted, thereby preventing the overcharging of the storage device.
Additionally, the input current into the storage device can be reduced without short-circuiting the generator, thereby preventing a deformation in the generated waveform and a reduction in the voltage level. Accordingly, the rotation period can be precisely controlled based on the generated waveform, thereby implementing the indication of the correct time.
In this case, the voltage of the storage device may preferably be detected at regular intervals.
With this arrangement, when the conducting state of the bypass circuit is controlled by the output of the storage device, the electrical energy required for controlling the bypass circuit switch can be reduced, thereby performing the efficient charging of the storage device.
The voltage may preferably be constantly detected when the detected voltage of the storage device exceeds the set value, and the voltage may preferably be detected at regular intervals when the detected voltage is not greater than the set value.
By constantly detecting the voltage when the detected voltage of the storage device exceeds the set value, the bypass circuit switch can be immediately turned off when the voltage is reduced to the set value or lower, thereby interrupting the current from flowing in the bypass circuit. It is thus possible to prevent the voltage of the storage device from being reduced to an excessively low value. Further, since the voltage detection circuit is driven at regular intervals when the voltage of the storage device is not greater than the set value, the current consumption when the voltage is low can be reduced, thereby efficiently charging the storage device. In particular, the voltage detection circuit is constantly driven only when the voltage of the storage device exceeds the set value and when an influence of power consumption is very little, thereby making it possible to efficiently control the power consumption.